+ =为运营商代表 [英] += operator for Delegate

问题描述

我知道，在 + = 运营商将一个方法添加到由代表基本对象保持调用列表，例如：

I know that the += operator will add a method to the invocation list maintained by the Delegate base object, for example

using System;

class Program
{

    delegate void MyDelegate(int n);

    void Foo(int n)
    {
        Console.WriteLine("n = {0}", n)
    }

    static void Main(string[] args)
    {
        MyDelegate d = new MyDelegate(Foo);
        d += Foo; // add Foo again

        d.Invoke(3); // Foo is invoked twice as Foo appears two times in invocation list

    }
}

两次

但是，当我看到MSDN 代表 MulticastDelegate 我找不到任何在 + = 运算符的定义。它是如何，这只是工作的？自动生成的编译器魔术

But when I look at MSDN Delegate, MulticastDelegate I can't find any definition of the += operator. How is it that is just works? Auto-generated compiler magic?

推荐答案

这不是在委托类型本身的运营商，在IL方面 - 它在语言定义规范，但你不会使用反射找到它。编译器把它变成一个电话 Delegate.Combine 。反向操作，使用 - 或 - = ，使用的 Delegate.Remove 。

It's not an operator on the delegate type itself, in IL terms - it's defined in the language specification, but you wouldn't find it using reflection. The compiler turns it into a call to Delegate.Combine. The reverse operation, using - or -=, uses Delegate.Remove.

至少，这是它是如何实现的。当C＃.NET的目标，因为它几乎总是这样。从理论上讲，这是环境特定的 - 语言规范并不要求编译器使用 Delegate.Combine 或 Delegate.Remove ，和不同的环境中可能不具有这些方法

At least, that's how it's implemented when C# targets .NET, as it almost always does. In theory, this is environment-specific - the language specification doesn't require that a compiler uses Delegate.Combine or Delegate.Remove, and a different environment may not have those methods.

从C＃5说明书中，部分7.8.4（加法）：

From the C# 5 specification, section 7.8.4 (addition):

二进制 + 运算符执行委托组合当两个操作数是一些委托类型 d的。 （如果操作数具有不同的委托类型，则发生绑定时错误）。如果第一个操作数是空，操作的结果是第二个操作数的值（即使那也是空）。否则，如果第二操作数是空，则操作的结果是所述第一操作数的值。否则，操作的结果是一个新委托实例，被调用时调用第一个操作数，然后调用第二个操作数。对于委托组合的示例，请参见§7.8.5和§15.4。由于 System.Delegate 不是委托类型，运营商 + 没有为它定义。

The binary + operator performs delegate combination when both operands are of some delegate type D. (If the operands have different delegate types, a binding-time error occurs.) If the first operand is null, the result of the operation is the value of the second operand (even if that is also null). Otherwise, if the second operand is null, then the result of the operation is the value of the first operand. Otherwise, the result of the operation is a new delegate instance that, when invoked, invokes the first operand and then invokes the second operand. For examples of delegate combination, see §7.8.5 and §15.4. Since System.Delegate is not a delegate type, operator + is not defined for it.

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